iceberg if this is a 10+ year old car that has never had any maintenance.

I went through a similar drill with a 1990 300SE.

The ignition on the M103 might need everything if it has never been maintained:

-rotor and cap, especially if the timing chain cover has leaked (and it does) which leads to an oily distributor cap, also the suppressor housings break down with heat and often crack when you remove them. Fixing the leak is documented in the wiki but takes time and patience.

-as noted, the plug wires will likely be fused to the plugs. Anticipate needing to cut them to remove and of course that means new wires. If you replace wires, getting them in the plastic cover is a pain and your back will ache from leaning over to work on it.

If there is oil leaking from the cam cover, you'll need to replace the gasket.

Transmission cooling hoses often develop leaks - easy to change but messy.

If you replace the serpentine ('poly V') belt, there is a possibility that the belt tensioner will be on its last legs and break leaving you with the prospect of replacing it before you can tension the belt. This is almost as much work as replacing the water pump. Mine was fine but others will tell you of problems.

I guess I'm suggesting that you be aware that cascading repairs often result from what looks to be a simple tune-up on a car that has lots of deferred maintenance and indifferent treatment.

The good news is that parts are very reasonable, both here at Fastlane or at other web vendors.